So I basically joined the site just to post in this topic after lurking since the leak.
Yes, I've experimented with ball-jointed waists, and they do eventually lose friction in heavier models, at least, the ones using these do. My Self-MOC (which I'll upload once I can get a good camera), however, uses these two parts and has remained sturdy since late 2009. Maybe the solution to this in a more practical sense would be some kind of ratcheting joint? TLG has used them before, the closest example being, I think, Exo-Force. Using these would allow them to pose at the waist while still maintaining stability.
However, something worth noting is that CCBS sets, at least of the standard HF size, look a lot better without waist articulation than later-year canister-scale Bionicle sets, and the same is true of the Avotoran builds. I look at my Tanma set (When his limbs haven't all fallen apart, that is), and he's just fine without a waist joint. I look at, say, Ackar, and he looks kinda awkward.
I'm already loving the hand sketch idea, looks awesome and functional. And it could be pretty universal: 'Villains' add the Viking horns, Toa leave them blank or use opaque Barraki eyes. Or you could use the HF claws that came on Core Hunter as a substitute for some sets.
My only beef with decreasing the size is that a lot of the older masks like the Olmak, Kraakhan, and Ignika are going to look really oversized on new sets. You could argue that it's okay, because they fit best on larger-scale characters, but for MOCing and playability's sake, it's bothering me a bit.
Also, got to agree with plot-relevant combiners. Yes, Stars gave us Gaardus, but that was a competition thing and his entrance and exit were so abrupt that the only surprise is that Greg didn't find some way to kill him off. Hell, I'm not even sure what size he's supposed to be. Is he to scale with his parts? Is he to scale with the 2006-2009 sets? Is he still Matoran-sized? Hell, screw just plot-relevant combiners, I want actual Kaita.
As for other things I want: No Glatorian and Agori. They were just less interesting than Toa and Matoran, with the whole "No powers unless Mata Nui headbutts your weapons" thing. and the fact that they're meant to be organic with cyborg implants isn't represented well by constraction sets. Looking at the various Ultrabuilds, from both Chima and Superheroes, they just look like robots with weirdly organic heads.
Some variation in Toa Teams: Fire, Air, Ice, Water, Stone, and Earth are great. However, Earth and Stone have a lot of overlap, especially after plant control got turned into its own element, whereas it's often the realm of Earth users. Added that we've got plenty of elements with no plastic representations yet... Remove either Earth or Stone, and replace with something else that hasn't had a set like Iron, or my personal favourite, Plasma.
A tone similar to the DCAU: Being my favourite animated series, I tend to take a little inspiration from Justice League, and I think it sort of fits.